Have you, which documentation was that? Is this server behind a NAT router or firewall? If it is, do you have a Split DNS configured (you should)? In any case, go to the 'Verify....' section of that article and provide the output of all the commands in that section.

The DOC is the Zimbra_NE_Quick_Start_8.0.pdf I downloaded it from Zimbra Site. Yes, the ZCS is behind a Firewall with NAT and Router....but released that message arrive in the Zimbra server so it's no problem with Firewall or DNS. I make sure done some test and that's ok regard DNS and Firewall. look the log please..